org.apache.bsf.engines.netrexx

Class NetRexxEngine

Implemented Interfaces:
BSFEngine, PropertyChangeListener

public class NetRexxEngine
extends BSFEngineImpl

This is the interface to NetRexx from the Bean Scripting Framework.

The NetRexx code must be written script-style, without a "class" or "properties" section preceeding the executable code. The NetRexxEngine will generate a prefix for this code:

 
 class $$CLASSNAME$$;
 method BSFNetRexxEngineEntry(bsf=org.apache.bsf.BSFManager) public static;
 
 
$$CLASSNAME$$ will be replaced by a generated classname of the form BSFNetRexx*, and the bsf parameter can be used to retrieve application objects registered with the Bean Scripting Framework.

If you use the placeholder string $$CLASSNAME$$ elsewhere in your script -- including within text strings -- BSFNetRexxEngine will replace it with the generated name of the class before the NetRexx code is compiled.

If you need to use full NetRexx functionality, we recommend that your NetRexx script define and invoke a "minor class", with or without the "dependent" keyword as suits your needs. You'll have to use $$CLASSNAME$$ in naming the minor class, since the name of the main class is synthesized; for example, to create the minor class "bar" you'd write "class $$CLASSNAME$$.Bar".

Hazards:

Since NetRexx has to be _compiled_ to a Java classfile, invoking it involves a fair amount of computation to load and execute the compiler. We are currently making an attempt to manage that by caching the class after it has been loaded, but the indexing is fairly primitive; we hash against the script string to find the class for it.

Minor-class .class files are now being deleted after the major class loads. This coould potentially cause problems.

Authors:
Joe Kesselman
Sanjiva Weerawarana

Field Summary

Fields inherited from class org.apache.bsf.util.BSFEngineImpl

classLoader, classPath, dbgmgr, declaredBeans, lang, mgr, tempDir

Constructor Summary

NetRexxEngine()
Constructor.

Method Summary

Object
call(Object object, String method, Object[] args)
Return an object from an extension.
void
declareBean(BSFDeclaredBean bean)
Object
eval(String source, int lineNo, int columnNo, Object script)
Override impl of execute.
void
exec(String source, int lineNo, int columnNo, Object script)
Override impl of execute.
Object
execEvalShared(String source, int lineNo, int columnNo, Object oscript, boolean returnsObject)
This is shared code for the exec() and eval() operations.
void
initialize(BSFManager mgr, String lang, Vector declaredBeans)
initialize the engine; called right after construction by the manager.
void
undeclareBean(BSFDeclaredBean bean)

Methods inherited from class org.apache.bsf.util.BSFEngineImpl

apply, compileApply, compileExpr, compileScript, declareBean, disconnectedDebuggerNotify, exec, getSpecificDebuggingInterface, initialize, placeBreakpointAtLine, placeBreakpointAtOffset, propertyChange, removeBreakpoint, setEntryExit, terminate, undeclareBean

Constructor Details

NetRexxEngine

public NetRexxEngine()
Constructor.

Method Details

call

public Object call(Object object,
                   String method,
                   Object[] args)
            throws BSFException
Return an object from an extension.
Specified by:
call in interface BSFEngine

Parameters:
method - The name of the method to call.
args - an array of arguments to be passed to the extension, which may be either Vectors of Nodes, or Strings.


declareBean

public void declareBean(BSFDeclaredBean bean)
            throws BSFException
Specified by:
declareBean in interface BSFEngine
Overrides:
declareBean in interface BSFEngineImpl


eval

public Object eval(String source,
                   int lineNo,
                   int columnNo,
                   Object script)
            throws BSFException
Override impl of execute. In NetRexx, methods which do not wish to return a value should be invoked via exec, which will cause them to be generated without the "returns" clause. Those which wish to return a value should call eval instead. which will add "returns java.lang.Object" to the header. Note: It would be nice to have the "real" return type avaialable, so we could do something more type-safe than Object, and so we could return primitive types without having to enclose them in their object wrappers. BSF does not currently support that concept.
Specified by:
eval in interface BSFEngine


exec

public void exec(String source,
                 int lineNo,
                 int columnNo,
                 Object script)
            throws BSFException
Override impl of execute. In NetRexx, methods which do not wish to return a value should be invoked via exec, which will cause them to be generated without the "returns" clause. Those which wish to return a value should call eval instead. which will add "returns java.lang.Object" to the header.
Specified by:
exec in interface BSFEngine
Overrides:
exec in interface BSFEngineImpl


execEvalShared

public Object execEvalShared(String source,
                             int lineNo,
                             int columnNo,
                             Object oscript,
                             boolean returnsObject)
            throws BSFException
This is shared code for the exec() and eval() operations. It will evaluate a string containing a NetRexx method body -- which may be as simple as a single return statement. It should store the "bsf" handle where the script can get to it, for callback purposes.

Note that NetRexx compilation imposes serious overhead -- 11 seconds for the first compile, about 3 thereafter -- but in exchange you get Java-like speeds once the classes have been created (minus the cache lookup cost).

Nobody knows whether javac is threadsafe. I'm going to serialize access to the compilers to protect it.


initialize

public void initialize(BSFManager mgr,
                       String lang,
                       Vector declaredBeans)
            throws BSFException
initialize the engine; called right after construction by the manager. Declared beans are simply kept in a vector and that's it. Subclasses must do whatever they want with it.
Specified by:
initialize in interface BSFEngine
Overrides:
initialize in interface BSFEngineImpl


undeclareBean

public void undeclareBean(BSFDeclaredBean bean)
            throws BSFException
Specified by:
undeclareBean in interface BSFEngine
Overrides:
undeclareBean in interface BSFEngineImpl